Channel | 100 mM KCl | 250 mM KCl | Mean |

WT (PA_{63})_{7} | 0.70 | 0.85 | 0.78 |

(PA_{63}E302S)_{7} | 0.60 | 0.83 | 0.72 |

(PA_{63}E343S)_{7} | 0.68 | 0.80 | 0.74 |

(PA_{63}D276S)_{7} | 0.70 | 0.74 | 0.72 |

(PA_{63}D335S)_{7} | 0.58 | 0.77 | 0.68 |

(PA_{63}E308S)_{7} | 0.55 | 0.72 | 0.64 |

(PA_{63}D315S)_{7} | 0.50 | 0.63 | 0.57 |

(PA_{63}F427A)_{7} | 0.38 | 0.48 | 0.43 |

Negative fixed charge density (molarity) of channels (calculated from Eq. 1) with [KCl]

= 100 and 250 mM KCl. Each entry is the value of [N] that fits the data in Figs. 2 and 3._{trans}